In numerous processes, effluent from a producer unit process is utilized as at least one feed component to a user unit process. This is particularly true in the petroleum and chemical industries. When plants including such unit processes are designed, they will normally be designed so that the effluent from the producer unit process will be essentially equal to the feed demands of the user unit process under normal operating conditions. Under these circumstances, it is preferred, in conventional practice, to pass the effluent from the producer unit process directly to the user unit process. However, this is not always possible, since the effluent flow will vary due to upsets in the operation of the producer unit process, normal fluctuations in the volume of effluent produced by the producer unit process, as to maintain proper heat balance, product purity, etc., and fluctuations in the production of effluent due to undesired variations in the feed flow thereto, the character of the feed, etc., while the user unit process requires a constant feed flow thereto for many of the same reasons, such as to maintain heat balance, product purity, etc. It is common practice to compensate for fluctuations in the rate of flow from the producer unit process by transmitting excess effluent from the producer unit process to a temporary storage unit, when the effluent flow rate exceeds the predetermined operating flow rate of feed to the user unit process, and to utilize the thus stored effluent, when the effluent produced is less than the predetermined flow rate to the user unit process. However, numerous problems are associated with the use of such temporary storage facilities. One major problem is that such temporary storage requires a flow line to the temporary storage unit and a flow line from the temporary storage unit. In many cases such flow lines must be constructed of expensive, specialized materials, thus substantially adding to the cost of plant construction and maintenance. In addition, it is necessary in such cases to maintain separate duplicative control systems for each of the two transmission lines, again, adding considerably to the expense of construction and maintenance.
Most importantly, the effluent from the producer unit process will normally be at an elevated temperature, at which temperature it is not possible to store the effluent. Accordingly, when effluent from the producer unit process is to be passed to temporary storage, it is normally cooled to a storage temperature prior to storage. As a result, addition of even small amounts of the thus cooled effluent, to make up deficiencies in the effluent produced by the producer unit process, causes serious upsets in the user unit process and lowers the capacity of the user unit process. It is, therefore, necessary in such cases to reheat the thus cooled effluent from the temporary storage unit prior to its use as a feed to the user unit process. Such cooling and reheating obviously adds to the cost of initial construction and operation of the plant and also results in substantial losses of heat and substantially increased energy requirements for reheating.